Mom drinks too much, fights on the phone too much and does a lot of nagging. Owen, who’s 12, but looks 10, suffers severe bullying at school “ the kind of torturous, homoerotic hazing that breeds both great stand-up comedy and mass murder “ and he’s taken to sitting alone in the apartment complex playground at night, singing to himself and eating candy.

When he’s not spying on neighbors with a telescope, he practices stabbing a penknife into a tree. When Abby (Chloe Moretz, “Kick-Ass”) moves in with her dad (Richard Jenkins, “Eat Pray Love”), Owen is creepy enough himself to willingly accept all the girl’s oddness.

She smells funny, doesn’t wear shoes in the snow, doesn’t go to school and only comes out at night. But she’s cute, and standoffish enough at first to hook Owen, who’s eager for a friend and, hopefully, a girlfriend.

It’s no spoiler to point out that Abby isn’t what she seems. Her demented thirst rests somewhere between vampire and chupacabra, and it’s Dad’s job to don a garbage bag mask, and head out in the shadows to help satiate her relentless bloodlust. It’s a thankless task, and his age means he’s getting careless and sloppy, enough so that a local cop (Elias Koteas, “Shutter Island”) is poking around, asking questions about missing persons and cold corpses.

“Let Me In” begins at the beginning of the end, backtracks a bit and carries through without answering all the questions. Director Matt Reeves (“Cloverfield”) wrote the screenplay, which was adapted from Sweden’s “Let the Right One In,” which in turn, was based on a novel by John Ajvide Lindqvist.

The film presents a slower burn than its trailer might have you believe. It’s more thriller than horror flick, and while it’s got bits of blood, it’s far from a bloodbath.

Smit-McPhee is perfectly cast. He’s simultaneously sympathetic and spooky; the kind of kid you would hug if you could avoid touching. Moretz is fantastic as well. She’s cute and creepy, and really sells the loneliness her character requires, which comes with an empty void that belies her youthful exterior.

Reeves is wise with his eye and the focus of every scene, which switches between central characters and fleeting shoots of scenes and atmospherics. Snow, sweaty window condensation and clutched hands do as much to sell the story as scenes with dripping veins and iridescent eyes. “Joe Wertz